Occupational Health and Safety Administration (OSHA) and Air Force Occupational Safety and Health (AFOSH) regulations require circuit breaker switches to be locked in the OFF position during servicing and/or maintenance of machines and equipment, such as aircraft. These regulations include OSHA standard 1910.147 and AFOSH standard 91-501, and require affixing of appropriate lockout devices to energy isolating devices during servicing and/or maintenance of machines and equipment.
Examples of circuit breaker switches traditionally employed for aircraft electrical systems include push/pull circuit breaker switches that are pulled outward to place the switch in the OFF position. Such push/pull switches may be locked out for servicing or maintenance by using a collar that is configured to be inserted under the push/pull switch to lock the switch in the OFF position by preventing the switch from being pushed in toward the ON position. The lockout collar may be removed following a servicing or maintenance operation so that the circuit breaker switch may then be pushed in to the ON position. Other types of circuit breaker lockout devices include those having a casing member having an opening that may be positioned around a conventional household circuit breaker toggle switch and having a set screw that may be driven into engagement with the circuit breaker toggle switch to secure the switch in the desired position. However, available lock out devices do not work well, if at all, with circuit breaker toggle switches having cylindrical switch arms, such as Military Standard MS24509 circuit breakers and similar circuit breakers having cylindrical switch arms.